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Glossary (M - R)
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M

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Magnetic field  The invisible force field cre­ated by a magnet.
Magnetron  A microwave vacuum tube that is a diode tube with built-in cavity resonators and an extremely powerful permanent magnet.
Manchester code  A type of the binary line code that prevents the DC voltage level on a transmission cable from building up to an unacceptable level. A unipolar or bipolar coding system widely used in LANs. Also called biphase encoding.
Marconi (ground-plane) vertical antenna  A quarter-wavelength vertical radiator used to achieve vertical polarization and omnidirec­tional characteristics. See also Quarter-wavelength vertical antenna.
Marker capability  The term describing the condition when a sweep generator has one or more reference oscillators that enable the response curve to be actively interpreted.
Matched line  The ideal situation in which a transmission line terminates in a load that has a resistive impedance equal to the char­acteristic impedance of the line.
Matching stub  SeeQ section.
Media Accesses Controller (MAC)  The cir­cuitry making up Layer 2 of an OSI type protocol.
Medium frequency (MF)  The frequency range from 300 to 3000 kHz.
MESFET  A junction field-effect transistor made with gallium arsenide (GaAs). Also called GASFET.
Metal-oxide-semiconductor field-effect transistor (MOSFET)  A transistor often used in switching amplifier applications. It provides extremely low power dissipation even with high current. The basic building block of most CMOS digital integrated circuits.
Metal-semiconductor field-effect transistor (MESFET)  See GaAsFET.
Metropolitan-area network (MAN)  A net­work that covers a city, town, or village. A cable TV system is an example of a MAN.
Microcom Networking Protocol (MNP)  A se­ries of protocols used with asynchronous modems that specify ways to handle error detection and correction and how to specify if data compression is used.
Micrometer (mm) or micron  One-millionth of a meter. Light waves or small dimensions in integrated circuits are expressed in terms of this unit.
Microstrip  A flat conductor separated from a conducting ground plane by an insulating dielectric used as a transmission line or tuned circuit. It is preferred for reactive circuits at microwave frequencies.
Microstrip tuned circuit  A section of microstrip transmission line used as a resonant circuit.
Microwaves  The frequencies from 1 GHz to 30 GHz.
Microwave antenna  Any antenna used at fre­quencies above 1 GHz.
Microwave transistor  A transistor that oper­ates like other transistors, whether it is a bipolar or an FET type. The differences between this and a lower-frequency transis­tor are geometry and packaging that is optimized for frequencies above 1 GHz.
Microwave transistor amplifier  The transistor amplifier used in the front end of a microwave receiver to provide initial amplification for the mixer. The typical gain range is 20 to 25 dB. Also a power transistor used in microwave transmitters.
Microwave tube  A type of tube that includes the klystron, magnetron, and traveling-wave tube.
Millimeter wave  An electromagnetic wave at a frequency above 40 GHz. The part of the frequency spectrum lower in frequency than x-rays but higher in frequency than mi­crowaves (about 30 to 300 GHz).
Minimum shift keying (MSK)  An improved version of FSK or continuous phase fre-quency-shift keying in which the signals are fully synchronized with one another.
Minor lobe  The portion of the directional re­sponse curve of an antenna that denotes the transmission of RF energy over a particular range of angles different from the major di­rection of radiation of the antenna.
Mixer (converter)  Any device or circuit whose output does not vary linearly with the input. A device that translates the signal up or down to another frequency.
MLT-3 encoding  The encoding method used in Fast Ethernet.
Mobile identification number (MIN)  The telephone number assigned to a cellular unit.
Mobile telephone switching office (MTSO)  The master control center to which the cells in a cellular phone system are connected by telephone lines or microwave radio relay links.
Modal dispersion  In a multimode step index cable, an attenuation or stretching of a pulse at the end of the cable.
Modem  A device that converts binary signals into analog signals capable of being trans­mitted over the telephone lines and demodu­lates them, re-creating the binary output.
Modulation  The process by which a baseband voice, video, or digital signal is modified by another, higher-frequency signal called the carrier.
Modulation index  The ratio of the frequency deviation to the modulating frequency.
Modulator  A circuit used to vary some aspect of a radio carrier or light signal in accordance with the modulating baseband signal.
Monochrome CRT  A black and white picture tube, a vacuum tube called a cathode-ray tube.
Monolithic microwave integrated circuit (MMIC)  A circuit that incorporates two or more stages of FET or bipolar transistors made on a common chip to form a multi­stage amplifier.
Morse code  A series of dots and dashes that represent letters of the alphabet, numbers, and punctuation marks.
MOSFET  See Metal-oxide-semiconductor field-effect transistor.
Motion Picture Experts Group (MPEG)  The organization that establishes technical stan­dards for movies and video.
m-law compander  The type of companding used in telephone systems in the United States and Japan.
Multicarrier modulation (MCM)  See Orthog­onal frequency division multiplexing.
Multicasting  The ability of IP to move fast audio and video data over the Internet from a single source to multiple destinations.
Multimode graded index cable  A type of ca­ble that has several modes, or paths, of trans­mission through the cable but is orderly and predictable.
Multimode step index cable  A type of cable used for short to medium distances at rela­tively low pulse frequencies. It is a widely used type of fiber-optic cable.
Multipath interference  Fading that occurs when a transmitted signal takes multiple paths to the receiver because of reflections. Also called Rayleigh fading.
Multiple data message format (MDMF)  A message format used in caller ID.
Multiple input multiple output (MIMO)  A wireless technique that makes use of multi­ple antennas at the transmitter and receiver to make use of multipath signals to improve communications range and reliability.
Multiplexer  A device or circuit that time- (or frequency-) shares a single channel with multiple signals.
Multiplexing  A technique which allows more than one signal to be transmitted concur­rently over a single medium.
Multistage integrated circuit amplifier  A type of small-signal microwave amplifier or monolithic microwave integrated circuit (MMIC).
Multistation access unit (MAU)  The basic wiring hub in a Token-Ring network.
Muting circuit  See Squelch circuit.
   

 

N

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N connector  Widely used in RF applications, this type of connector is used on larger cables such as RG-8/U.
Nanometer (nm)  One-billionth of a meter. Light waves are often expressed in terms of nanometers.
Narrow-band FM (NBFM)  A special case of FM in which the modulation process produces only a single pair of significant sidebands like those produced by AM.
National Telecommunications and Information Administration (NTIA)  A regulatory body of the U.S. government whose function is to regulate electromagnetic emissions for the government and military services.
Navigation satellite  A satellite that provides accurate position information to ships, air­planes, and land-based vehicles.
Near field  The radio wave within about one wavelength of the radiating antenna.
Near field communications (NFC)  A short range wireless technology similar to RFID that uses the near magnetic field of a radio wave for data transfers at distances to 8 inches. Used for payment and access when used in a cell phone.
NE566 IC VCO  An IC voltage-controlled oscillator.
NE602 IC mixer  A popular circuit that uses bipolar transistors connected as Gilbert transconductance cells.
Network analyzer  A test instrument designed to analyze linear circuits. It is a combination instrument that contains a wide-range sweep sine-wave generator and a CRT output that displays not only frequency plots like a spec­trum analyzer but also plots of phase shift versus frequency.
Network attached storage (NAS)  A group of hard disks usually connected to a computer or server via standard Ethernet.
Network interface card (NIC)  A device that provides the I/O interface between each node on a network and the network wiring.
Neutralization  A process through which one signal, equal in amplitude to an original sig­nal, is fed back, resulting in the two signals canceling one another.
Noise  In electronics, any signal that is a mixture of many frequencies at many amplitudes that gets added to a radio or information signal as it is transmitted from one place to another or as it is processed. Random signal variations picked up by a receiver or caused by thermal agitation and other conditions inside the re­ceiver circuitry. Random, undesirable elec­tronic energy that enters a communication system via the communication medium and interferes with the transmitted message.
Noise bridge  A bridge circuit driven by a ran­dom noise voltage source that has an antenna or coaxial cable as one leg of the bridge. Used to make antenna characteristic imped­ance measurements and measurements of coaxial cable velocity factor and length.
Noise factor  The ratio of the S/N power at the input to the S/N power at the output.
Noise figure  The noise factor as expressed in decibels.
Noise immunity  Resistance to noise. Digital signals are more immune to noise than analog signals.
Noise margin  The amount of voltage between the highest expected noise voltage and a threshold level above which triggering occurs.
Noise temperature  Another way to express noise in an amplifier or receiver using the Kelvin scale.
Nonreturn to zero encoding (NRZ)  A method of encoding in which the signal remains at the binary level assigned to it for the entire bit time.
North American TDMA (NA-TDMA)  SeeIS136TDMA.
Notch, band-reject, or bandstop filter  A type of filter that rejects or stops frequencies over a narrow range but allows frequencies above and below to pass.
Number assignment module (NAM)  A pro­grammable read-only (PROM) chip in a cel­lular radio.
Numerical aperture (NA)  A number less than 1 that indicates the range of angles over which a particular cable will work.
Nyquist frequency  The minimum sampling frequency at which the high-frequency infor­mation in an analog signal can be retained. It is equal to two times the highest signal frequency.
   

 

O

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Octet  An 8-bit number, word or block of data. Another name for byte.
Omnidirectional antenna  An antenna that transmits equally well in all horizontal direc­tions. It has a circular horizontal transmis­sion pattern.
One-shot multivibrator  A pulse generator cir­cuit that produces one output pulse whose du­ration has been set to some desired interval.
ON–OFF keying (OOK)  A form of amplitude modulation where the carrier is turned off or on by a modulating binary signal.
Open systems interconnection (OSI) protocol  A framework or hierarchy designed to estab­lish general interoperability guidelines for developers of communication systems and protocols.
Optical communication system  A communi­cation system that uses light to transmit in­formation from one place to another.
Optical-electrical-optical (OEO) conversion  See Regeneration.
Optical signal analyzer  An optical test in­strument that provides the OTDR measure­ment and is also a sampling oscilloscope capable of displaying signals of more than 10 Gbps.
Optical spectrum  A group of signals with fre­quencies higher than 300 GHz. The range of frequencies that consists of infrared, visible, and ultraviolet light (range of 3 1011 to 3 1016 Hz).
Optical time domain reflectometer (OTDR)  A device that generates a light pulse and sends it down a fiber-optic cable to be tested. If there is a defect in the line, light will be reflected. The time between the generated and reflected pulses is measured.
Optics  The aspect of physics concerned with the behavior of light.
Orbit  The path taken by a satellite as it circles the earth.
Orthogonal frequency division multiplexing (OFDM)  A modulation method by which data is transmitted by simultaneously modu­lating segments of the high-speed bit stream onto multiple carriers spaced throughout the channel bandwidth. Also called multicarrier modulation (MCM).
Oscillator diode  A special semiconductor de­vice (Gunn diode, TRAPPAT diode, etc.) that generates a microwave signal, usually a sine wave at the resonant frequency, when used with a tuned circuit element such as a wave­guide, microstrip, microstrip, or stripline.
Overmodulation  In amplitude modulation, the term describing the condition when the mod­ulating voltage is greater than the carrier voltage.
Overranging  In amplitude modulation, the condition that occurs when the count capa­bility of a counter is exceeded during the count interval.
Oversampling converter  A type of converter that uses a clock or sampling frequency that is many times the minimum Nyquist rate re­quired for other types of converters. The ¢ converter is an example of an oversampling converter.
Overtone  Similar to a harmonic. An integer multiple of a fundamental oscillation frequency.
Overtone crystal  A crystal that is cut in a spe­cial way so that it optimizes its oscillation at an overtone of the basic crystal frequency.
Overvoltage protection  The protection af­forded by circuits and components that pro­tect the subscriber line interface circuits from electrical damage.
   

 

P

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Packet  A unit of data made up of the frame of data and additional bytes at the beginning and end that contain addresses and error cor­rection codes.
Paging receiver  A small, battery-operated su­perheterodyne receiver that enables individu­als to be signaled, wherever they may be.
Paging system  A popular communication sys­tem that operates in the simplex mode, for it broadcasts signals only to small battery-operated receivers.
PAM demultiplexer  A circuit that recovers data multiplexed with PAM.
PAM/FM system  An arrangement in which PAM signals frequency-modulate a carrier.
PAM/FM/PM system  An arrangement in which PAM signals frequency-modulate a subcarrier that, in turn, phase modulates the carrier.
Parabolic antenna  An antenna in which the energy radiated by the horn is pointed at a parabolic reflector that focuses the energy into a narrow beam and reflects it toward its destination. When receiving, the antenna focuses signals on the horn.
Parallel data transmission  A type of data transfer in which all the bits of a code word are transferred simultaneously. This method of data transfer is not practical in long-distance communication systems.
Parallel resonant circuit  A selective circuit formed when the inductor and capacitor are connected in parallel with the applied voltage.
Parallel-wire line  A transmission line made up of two parallel conductors separated by a space of 1⁄2 in. to several inches.
Parasitic array  A basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line. A Yagi antenna.
Parasitic oscillation  A type of abberant oscil­lation that occurs when a circuit oscillates at a higher frequency unrelated to the tuned frequency.
Parity  A widely used system of error detec­tion. Each character transmitted contains 1 additional bit.
Passband  The frequency range over which a filter or amplifier passes signals. This is the range between cutoff frequencies or between the cutoff frequency and zero.
Patch antenna  An antenna made with mi­crostrip on PCBs. It is a circular or rectangu­lar area of copper separated from the ground plane by the thickness of the PCB’s insulat­ing material.
Path attenuation  Loss created by the distance of free space between a transmitting and re­ceiving antenna, usually expressed as a power ratio or in decibels.
Pattern generator  A device that produces fixed binary bit patterns in serial form to use as test signals in data communication systems.
PCM demultiplexer  A circuit that recovers data multiplexed using PCM.
Peak envelope power (PEP)  The maximum power produced on voice amplitude peaks in single sideband communication.
Peer-to-peer configuration  A type of LAN that is smaller and less expensive than client-server LANs and provides a simple way to build a network within an office.
Percentage of modulation  The ratio of the amplitude of the modulating signal to the amplitude of the carrier.
Perigee  Lowest point of a satellite orbit above the earth.
Permittivity  The dielectric constant of the ma­terial between two conductors.
Personal-area network (PAN)  A very small network created informally or on an ad hoc basis. Nowadays, all PANs are wireless.
Personal communication service (PCS)  The band of frequencies near 1900 MHz that is used for cellular telephones.
Phase modulation (PM)  The signal that re­sults when the amount of phase shift of a constant-frequency carrier is varied in accor­dance with a modulating signal.
Phase modulator  A circuit often used instead of direct FM because the carrier oscillator can be optimized for frequency accuracy and stability.
Phased array  An antenna system made up of a large group of similar antennas on a common plane to provide controllable gain and directivity.
Phased array radar  A type of radar that pro­vides flexibility in scanning narrow sectors and tracking multiple targets by using a phased antenna array.
Phase-locked loop (PLL)  A frequency- or phase-sensitive feedback control circuit used in frequency demodulation, frequency syn­thesizers, and various filtering and signal-detection applications.
Phase-shift keying (PSK)  A type of modula­tion in which the binary signal changes the phase shift of a sine-wave character depend­ing upon whether a binary 0 or a binary 1 is to be transmitted. Also called binary phase-shift keying (BPSK).
Phasor  A line or arrow whose length is pro­portional to the peak value of the sine wave being represented and its angle indicating phase position.
Photocell  See Light detector.
Photodiode  Silicon PN-junction diode that is sensitive to light. It is the most widely used light sensor.
Phototransistor  A light-sensitive transistor used for light detection.
Physical optics  A term referring to the ways that light can be processed.
PHY  Abbreviation of the physical layer of a data communications system based on the OSI system.
pnetwork  Network configuration resembling the Greek letter p.
p/4-DQPSK modulation  A method of modu­lation used in IS-136 TDMA.
Piconet  The linking of one Bluetooth device that serves as a master controller to up to seven other Bluetooth devices.
Pierce oscillator  An oscillator configuration using field-effect transistors or bipolar tran­sistors with crystals.
Piezoelectric effect  Vibration that occurs when a crystal is excited by an AC signal across its plates.
Pilot carrier  A low-level carrier signal. It is used to help in the recovery of DSB and SSB signals.
PIN diode  A device used as a switch or vari­able resistor in a microwave circuit. This PN-junction diodes has an I layer between the P and N sections.
PIN diode modulator  A modulator using a special type of silicon junction diode de­signed for use at frequencies above approxi­mately 100 MHz.
Pixel  A tiny dot of light, thousands of which make up a television or computer monitor screen. Each pixel can be any of hundreds of colors.
PL-259 connector  A male connector that fits on the end of a coaxial cable and provides a way to attach the shield braid and inner conductor.
Plaintext  The name given to any message or data to be encrypted.
Plan-position indicator (PPI)  A type of CRT display that shows both the range and the azimuth of a target on a radar set.
Plenum cable  Coaxial or twisted-pair cable run between floors and across ceilings through special channels or chambers built into the structure.
PLL demodulator  A circuit that recovers FM signals. It has an S/N ratio better than that of other FM detectors.
Point-contact diode  A semiconductor diode made from a piece of P-type semiconductor material and a fine tungsten wire that makes contact with the semiconductor material at a small point of contact. Used in radar receivers.
Point of presence (POP) office  A serving office used to provide interconnections to the IXCs.
Polar orbit  A satellite orbit that passes over the north and south poles.
Polarization  The orientation of the electric field in a radio wave with respect to the earth.
Pole  A frequency at which there is a high im­pedance in the circuit.
Posigrade orbit  An orbit that moves in the same direction as the earth’s rotation.
Power (flux) budget  An accounting of all at­tenuation and gain in a fiber-optic system.
Power combiner  A component, circuit, or waveguide assembly that sums the power outputs of two or more circuits.
Power divider  A component, circuit, or wave­guide assembly that equally divides a com­mon input amongst two or more outputs.
Power meter  A commonly used RF test meter that measures the forward and reflected power output of a circuit.
Power subsystem  The basic power source of a satellite system. Most satellites use solar panels for its basic power source.
Preamble  Multiple bytes of data in a packet protocol that help to establish clock synchronization.
Pre-emphasis  A technique that helps to offset high-frequency noise interference in FM radio.
Prescaler  A special frequency divider nor­mally used between the high-output fre­quency of a VCO and the programmable part of a divider in a PLL frequency synthesizer. Also a divider used ahead of a frequency counter.
Prescaling  A frequency division technique that involves the division of the input frequency by a factor that puts the resulting signal into the normal frequency range of the counter.
Primary rate interface (PRI)  An ISDN con­nection type made up of one twisted pair. This method uses 23 bearer (B) channels and one (D) channel multiplexed on the line.
Prime meridian  Special meridian used as a reference point for measuring longitude.
Private automatic branch exchange (PABX)  A telephone switching system that is extremely small, fast, and efficient. Many PABXs are designed to carry digital signals and analog voice signals.
Private branch exchange (PBX)  A telephone switching system, dedicated to a single cus­tomer, which provides telephone switching and links inside an organization and also connects to the standard public telephone network.
Private telephone system  Telephone service provided to companies or large organizations with many employees and many telephones.
Product detector  A balanced modulator used to recover SSB or DSB signals.
Progressive scanning  Line-after-line scanning used in HDTV and computer monitor screens.
Protocol  Rules and procedures used to ensure compatibility between the sender and re­ceiver of serial digital data.
Protocol analyzer  A test instrument used to capture and analyze the data transmitted in a data communication system.
Public key encryption (PKE)  A method of en­cryption that uses two keys, one public and the other private.
Pulse-amplitude modulation (PAM)  Modula­tion that produces a series of constant-width pulses whose amplitudes vary with the ana­log signal. The pulses are usually narrow compared to the period of sampling.
Pulse-averaging discriminator  A circuit that converts FM signals into constant-amplitude pulses and filters them into the original signal.
Pulse-code modulation (PCM)  A form of time division multiplexing (TDM) in which multiple channels of digitized voice signals are transmitted in serial form. Each channel is assigned a time slot in which to transmit one binary word of data.
Pulse dialing  The type of dialing produced by a rotary dialing mechanism in older tele­phones.
Pulse-duration modulation  See Pulse-width modulation.
Pulse modulation (PM)  Modulation used to transmit analog data in the form of pulses whose amplitude, width, or time position is varied.
Pulse-position modulation (PPM)  A procedure in which the pulses change position according to the amplitude of the analog signal.
Pulse spectrum  The frequency distribution of the sinusoidal components of a pulse in rela­tive amplitude and relative phase.
Pulse-width modulation (PWM) or pulse-duration modulation (PDM)  A procedure in which the width or duration of the pulses varies according to the amplitude of the ana­log signal.
Pulsed radar  A radar system in which signals are transmitted in short bursts or pulses.
Push-pull amplifier  An amplifier using two tubes or transistors biased for Class AB, B, or C, connected in such an arrangement that both the positive and the negative alterna­tions of the input are amplified.
   

 

Q

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Q  The quadrature signal is an I-Q modulator.
Q color signal  A TV color signal with the fol­lowing specifications: 21 percent red, 52 percent green, 31 percent blue.
Q section (matching stub)  A quarter wave­length of coaxial or balanced transmission line of a specific impedance that is con­nected between a load and a source in order to match impedances.
Quadrative  A 90° phase relationship.
Quadrature amplitude modulation (QAM)  A modulation technique used in modems for increasing the number of bits per baud. It uses both amplitude and phase modulation of a carrier.
Quadrature detector  An FM demodulator that produces a phase shift of 90° at the un­modulated carrier frequency. It is primarily used in TV audio demodulation.
Quadrature modulation  A type of modula-tion-multiplexing that combines two carriers shifted by 90°, each modulated by a separate signal.
Quadrature (quaternary or quadra) phase PSK (QPSK or 4-PSK)  A system in which each pair of successive digital bits in the transmit­ted word is assigned a particular phase. It is used to increase the binary data rate while maintaining the bandwidth needed to trans­mit the signal.
Quantizing error  Error associated with the analog-to-digital conversion process.
Quarter-wavelength vertical antenna  An an­tenna whose main radiating element is a wire, tubing, or conductor that is one-quarter wavelength at the main operating frequency. Also called a Marconi or ground-plane antenna.
Quieting method  A type of sensitivity mea­surement that determines the amount of RF input signal needed to reduce output noise to 20 dB.
   

 

R

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R - Y signal  A color signal also called B - Y. Com-bining three color signals causes Y to be subtracted from R or B signals.
Radar (radio detection and ranging)  An electronic communication system based on the principle that high-frequency RF signals are reflected by conductive targets.
Radial  A quarter-wavelength wire laid hori­zontally on the ground or buried in the earth at the base of an antenna to create an artifi­cial ground plane.
Radiation resistance  The impedance of an an­tenna at its driving point.
Radio  The general term applied to any form of wireless communication from one point to another.
Radio frequency identification (RFID)  A grow­ing wireless technique similar to bar coding.
Radio horizon  The distance at which direct wave signals can no longer be received. It is a function of the height of the transmitting and receiving antennas.
Radio wave  An electromagnetic wave that can be reflected, refracted, diffracted, and focused.
Rayleigh fading  See Multipath interference.
RC filter  A filter using combinations of resis­tors and capacitors to achieve the desired frequency response.
RCA phonograph connector  An inexpensive coaxial connector used primarily in audio equipment.
Reactance  The opposition to AC flow that is offered by coils and capacitors.
Reactance modulator  A circuit that uses a transistor amplifier that acts like either a variable capacitor or an inductor to produce direct FM.
Receive signal strength indicator (RSSI) signal  In the analog AMPS cellular telephone sys­tem, a signal sent back to the cell site so that the mobile telephone switching office (MTSO) can monitor the received signal from the cell and decide whether to switch to another cell.
Receiver  The speaker in a telephone handset. A collection of electronic components and circuits that accepts the transmitted message from a channel and converts it back to a form understandable by people. A device in which a modulated light wave is picked up by a photodetector. The signal is amplified and then demodulated to recover the original signal.
Redundancy  The simplest way to ensure error-free transmission. Each character or message is sent multiple times until it is properly received.
Redundant array of independent disks (RAID)  A collection of hard disk drives used to store data remotely from a computer or server.
Reed Solomon  A widely used forward error correction technique that encodes and de­codes both wired and wireless data streams to improve reliability of data transfer.
Reed-Solomon (RS) code  A forward error correction code that adds extra parity bits to the block of data being transmitted. It per­mits multiple errors to be detected and corrected.
Reference regulator  A zener diode that re­ceives the DC supply voltage as an input and translates it into a precise reference voltage.
Reflected power  The power not absorbed by a load and bounced back to the transmitter.
Reflection  When light rays strike a reflective surface, the light waves are thrown back, or reflected. The angle of reflection is equal to the angle of incidence. Radio waves are re-flected by any conducting surface they encounter along a path.
Reflection coefficient  The ratio of the re­flected voltage wave Vr to the incident volt­age wave Vl. It provides information on current and voltage along a transmission line.
Reflector  A parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element. A parabolic dish used in microwave antennas.
Refraction  The bending of a light ray that oc­curs when light rays pass from one medium to another. The bending of radio waves in the ionosphere.
Regeneration  The process of converting a weak optical signal to its electrical equiva­lent, amplifying and reshaping it electroni­cally, and then retransmitting it on another laser. Also used to rejuvinate electrical sig­nals transmitted over long distances.
Regenerative repeater  A circuit that picks up transmitted signals, amplifies them, and retransmits them sometimes on another frequency.
Remote bridge  A special bridge used to con­nect two LANs that are separated by a long distance.
Repeater  A circuit that takes a partially de­graded signal, boosts its level, and shapes it up. Over long distances, several repeaters may be required. A satellite used to receive information from a transmitting station and then retransmit it to receiving stations.
Resolution  The amount of detail produced by a TV signal. In D/A converters, the total number of increments the D/A converter produces over its output voltage range.
Resonant circuit  A tuned circuit or filter that has a maximum response, either voltage or current, at a particular (resonant) frequency. A circuit using a combination of inductance and capacitance or materials that exhibits resonance such as ceramic or quartz crystals.
Retrograde orbit  The orbit that moves in the direction opposite to the earth’s rotation.
Return to zero (RZ) encoding  A method of encoding in which the voltage level assigned to a binary 1 level returns to zero during the bit period.
Reverse AGC  A method of reducing gain by decreasing the collector current.
RF amplifier  Also known as a preselector, or low-noise amplifier that provides some ini­tial gain and selectivity in a receiver.
RF probe (detector probe)  A rectifier with a filter capacitor that stores the peak value of the sine-wave RF voltage.
RF signal generator  A signal generator used in testing. A variable-frequency oscillator or a frequency-synthesizer.
RF voltmeter  A special piece of test equip­ment optimized for measuring the voltage of high-frequency signals.
RG-8/U coaxial cable  One of two types of coaxial cable used in Ethernet networks and antenna transmission lines. It has a charac­teristic impedance of 53 , is about 0.4 in. in diameter, and is referred to as thick cable.
RG-58/U coaxial cable  A widely used thin cable, this cable is used for antenna trans­mission lines for CB radios and cellular telephones as well as for LANs.
Right-hand circular polarization (RHCP)  The term that describes radiation which leaves an antenna with a clockwise rotation.
Ring  A terminal on a telephone at which wires end.
Ring topology  A LAN configuration in which one PC acts as a server and the computers are linked together in a closed loop. Data is usually transferred around the ring in only one direction, passing through each node.
Ringer  A bell or electronic oscillator con­nected to a speaker that is used to indicate the presence of an incoming call.
Ringing  A 20 Hz signal provided by a local telephone office that indicates when a spe­cific telephone is receiving a call.
Ripple  Amplitude variation with frequency in the passband, or the repetitive rise and fall of the signal level in the passband of some types of filters.
Rise time  The time it takes a pulse voltage to rise from its 10 percent value to its 90 per­cent value.
RJ-11 connector  A modular plug containing up to six terminals through which most tele­phones attach to an outlet.
RJ-45 connector  A large modular connector used in terminating twisted pairs in Ethernet LANs. It contains up to eight terminals.
Root-mean-square (rms)  An average that ex­presses current or voltage magnitude.
Router  An intelligent device with decision-making and switching capabilities, designed to connect two networks.
Rubbering  A term sometimes applied to the whole process of fine-tuning a crystal in an oscillator.







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